EP0351337A1 - Moulding compositions based on thermotropic polymers reinforced with mineral fillers - Google Patents

Abstract

The present invention relates to compositions capable of being employed for making moulded objects, comprising a thermotropic polymer and a particular inorganic reinforcing filler. <??>According to the invention the inorganic filler corresponds to the following definitions: . it belongs to the class of crystalline inorganic fillers of platelet shape which have a mean diameter which lies in the range from 0.5 to 400  mu m and a shape factor represented by the relationship: mean particle diameter in mu m/mean particle thickness in mu m which lies in the range from 10 to 90; . it is introduced by employing use quantities, expressed in % by weight of filler in the combination of polymer + filler, which lie in the range from 20% to 60%, with the additional condition according to which these quantities lie in the ranges from a value above 50% to 60% when the mean particle diameter is smaller than 20  mu m. <??>The moulded objects obtained from these compositions exhibit improved mechanical properties whose anisotropy is greatly reduced.

Description

The present invention relates to compositions, which can easily lead to shaped articles by molding from the molten state, comprising a thermotropic polymer and an inorganic reinforcing filler specially adapted for this thermotropic polymer. It also relates to the shaped articles produced from these compositions.

Over the past ten years, there has been an increasing interest in thermotropic polymers. This interest is linked to the fact that these polymers are capable of forming anisotropic melts which have their own orientation and a relatively high degree of organization. This orientation and this organization are found in molded objects by giving them (already in the raw state) improved mechanical properties (in particular in terms of modulus and flexural strength) which are not usually observed on products. crude isotropic. But in certain circumstances, a disadvantage of the objects molded from an anisotropic melt, which appears, lies in the non-equilibration (or anisotropy) of the longitudinal properties (in the direction of the flow of the melt which is by example the direction of injection in the case of an injection molding) and transverse properties (in the direction perpendicular to that of the flow).

It is known to reduce the anisotropy of polymeric materials by adding mineral fillers.

dans lequel les modules sont mesurés dans les conditions définies ci-après dans le présent mémoire, est réduit d'au moins 50 % par rapport à ce qui se passe avec le polymère non chargé, et
- la somme ML + MT est au moins égale à 1,5 fois la valeur de la même somme obtenue dans le cas du polymère non chargé.A first object of the present invention is to provide compositions comprising a thermotropic polymer with a specially adapted mineral filler which make it possible to produce shaped articles having simultaneously the following two properties:
- the anisotropy report (AR) which is represented by the following report:

in which the modules are measured under the conditions defined below in this specification, is reduced by at least 50% compared to what happens with the uncharged polymer, and
- the sum ML + MT is at least equal to 1.5 times the value of the same sum obtained in the case of the uncharged polymer.

The reduction rate of the RA is calculated by applying the following usual relation:

We also know that, to make shaped articles by molding, we must avoid using too large quantities of fillers - such as those greater than 60% by weight of filler, relative to the polymer + filler assembly - so that the fillers do not play a detrimental role on the surface condition properties and on the dimensional stability of the articles obtained. In addition, it is known that highly charged polymers have too high a viscosity in the molten state to allow precision molding with, if necessary, a good impression rendering.

Another object of the present invention is to provide compositions which make it possible to produce shaped articles whose combination of properties set out above is obtained with quantities of fillers which remain less than or equal to 60% by weight.

In document EP-A-0.044.147, it has been proposed to reduce the anisotropy of thermotropic polymers by adding inert fibrillary charges having an acicular form such as for example short glass fibers or wollastonite, but it has been found that the goals in terms of anisotropy (RA and sum ML + MT) and of quantity of charge, which have been defined above, cannot be achieved in conjunction with such charges.

It has now been found that all of the goals defined above can be achieved thanks to the judiciously chosen compositions, the description of which will follow.

• a) un polymère thermotrope, et
• b) une charge minérale de renforcement,

caractérisées en ce que la charge minérale (b) répond aux définitions suivantes :
. elle appartient à la famille des charges minérales cristallines de forme plaquettaire ayant un diamètre moyen qui se situe dans l'intervalle allant de 0,5 à 400 µm et un facteur de forme représenté par le rapport :

qui se situe dans l'intervalle allant de 10 à 90 ;
. elle est mise en oeuvre en utilisant des quantités d'emploi, exprimées en % en poids de charge dans l'ensemble polymère + charge, qui se situent dans l'intervalle allant de 20 % à 60 %, avec la condition complémentaire selon laquelle ces quantités se situent dans l'intervalles allant d'une valeur supérieure à 50 % jusqu'à 60 % quand le diamètre moyen des particules est inférieur à 20 µm.More specifically, the present invention relates to molding compositions which comprise:

• a) a thermotropic polymer, and
• b) a mineral reinforcing filler,

characterized in that the mineral filler (b) meets the following definitions:
. it belongs to the family of crystalline mineral fillers of platelet form having an average diameter which is in the range from 0.5 to 400 μm and a form factor represented by the ratio:

which is in the range of 10 to 90;
. it is implemented using use quantities, expressed in% by weight of filler in the polymer + filler assembly, which are in the range from 20% to 60%, with the additional condition that these quantities are in the range from a value greater than 50% up to 60% when the average particle diameter is less than 20 µm.

Thermotropic polymers which are suitable for the implementation of the present invention include fully aromatic polyesters, alkyl aromatic polyesters, fully aromatic polyesteramides, alkylaromatic polyesteramides, aromatic polyazomethines, aromatic polyester carbonates and mixtures of these polymers.

According to a preferred embodiment of the present invention, the thermotropic polymers which are used are fully aromatic polyesters, fully aromatic polyesteramides and mixtures of these polymers.

Fully aromatic polyesters which are thermotropic, that is to say which are capable of forming anisotropic melts are described for example: in US Pat. Nos. 3,991,013, 3,991,014, 4,066,620, 4,075,262 , 4.118.372, 4.130.545, 4.161.470, 4.181.792, 4.188.476, 4.219.461, 4.224.433, 4.230.817, 4.346.208; in the European patent application No. 86420013.4 published under No. 0.191.705; and in French patent application No. 87/10177 filed on July 10, 1987 by the Applicant; the substance of these patents or patent applications is incorporated herein by reference.

Fully aromatic polyesteramides which are thermotropic are described, for example: in US Pat. Nos. 4,272,625, 4,330,457, 4,339,375, 4,355,132; in European patent application No. 87420327.6 published under No. 0.272.992; and in French patent applications Nos. 87/10177, 87/10178 and 87/10179 filed on July 10, 1987 by the Applicant; the substance of these patents or patent applications is incorporated here also by reference.

The thermotropic polymers which are chosen for the implementation of the present invention are those, belonging to the above-mentioned general or preferred families, which have a flow temperature lying in the range from 200 ° C. to 350 ° C. and, preferably ranging from 260 ° C to 330 ° C and which have an inherent viscosity at least equal to 0.5 dlg⁻¹ and preferably lying in the range from 1.0 to 4.0 dlg⁻¹. The term "flow temperature" is understood to mean the temperature at which the edges of a sample in the form of a polymer chip or cut fiber begin to round; this temperature is determined by visual observation of the sample on a coverslip for an appropriate temperature rise rate generally of the order of 10 ° C to 20 ° C per minute, observation made using a microscope equipped with a heating stage known in the trade under the brand THERMOPAN. Regarding the inherent viscosity, it should be noted that it is measured at 25 ° C on a solution containing 0.5 g of polymer per 100 cm³ of a solvent mixture parachlorophenol / 1,2-dichloroethane (50/50 by volume ).

• (I) désignant la stucture :
  
  dans laquelle R₁ représente un radical méthyle ou éthyle ou un atome de chlore ou de brome, les unités (I) pouvant être identiques ou différentes entre elles,
• (II) désignant la structure :
  
• (III) désignant la structure :
  
• (IV) désignant la structure :
  
  dans laquelle le symbole A représente un atome d'oxygène ou le groupement NH ;

- le rapport molaire des unités (I) par rapport à la somme des unités (II) + (III) se situe dans l'intervalle allant de 0,95 à 1,05 ;
- la quantité des unités (II) dans le mélange (II) + (III) se situe dans l'intervalle allant de 0 à 70 % en mole et celle des unités (III), par rapport à la même référence, se situe dans l'intervalle allant de 100 à 30 % en mole ;
- la quantité des unités (IV), exprimée par rapport à la quantité des unités (I), se situe dans l'intervalle allant, dans le cas où A = O, de 10 à 300 % en mole et, dans le cas où A = NH, de 5 à 100 % en mole.Fully aromatic thermotropic polyesters and polyesteramides which are especially preferred for the implementation of the present invention are those described in European patent applications No. 86420013.4 (published under No. 0.191.705) and No. 87420327.6 (published under No. 0.272.992). These polyesters and polyesteramides have the following particularities:
- they include recurrence units of formula (I), (II), (III) and (IV), the presence of the units (II) being optional:

• (I) designating the structure:
  
  in which R₁ represents a methyl or ethyl radical or a chlorine or bromine atom, the units (I) possibly being identical or different between them,
• (II) designating the structure:
  
• (III) designating the structure:
  
• (IV) designating the structure:
  
  in which the symbol A represents an oxygen atom or the NH group;

- The molar ratio of the units (I) to the sum of the units (II) + (III) is in the range from 0.95 to 1.05;
- the quantity of the units (II) in the mixture (II) + (III) is in the range from 0 to 70 mol% and that of the units (III), relative to the same reference, is in the range from 100 to 30 mol%;
- the quantity of the units (IV), expressed in relation to the quantity of the units (I), lies in the range going, in the case where A = O, from 10 to 300 mol% and, in the case where A = NH, from 5 to 100% by mole.

According to an even more particularly preferred form, the aromatic polyesters and polyesteramides which can be used in the present invention have a structure such as that defined above in which:
- the quantity of the units (II) in the mixture (II) + (III) is in the range going from 20 to 60 mol% and that of the units (III), compared to the same reference, goes from 80 40% by mole,
- and the quantity of the units (IV), expressed in relation to the quantity of the units (I), lies in the interval going, in the case where A = O, of 30 at 200% by mole and, in the case where A = NH, from 10 to 60% by mole. Among the polyesters and aromatic polyesteramides corresponding to this even more especially preferred modality, those which are very suitable are polymers having a structure in which the units (I) are identical, with the substituent R₁ representing a methyl radical or a chlorine atom.

et R₃, qui peuvent être identiques ou différents, ont chacun la définition donnée ci-avant pour R₁, les unités (I˝) pouvant être identiques ou différentes entre elles,

symbole A a la signification donnée ci-avant à propos des unités (IV).The very preferred aromatic polyesters and polyesteramides which have just been mentioned also include polymers which may also contain in their structure aromatic units generating ester and amide functions (dioxy units and / or dicarbonyl units and / or mixed oxy / carbonyl units or amino-secondary / carbonyl) having a structure other than that of units (I), (II), (III) and (IV), the total amount of these additional units being at most equal to 10% by mole relative to the quantity of units (I). A non-exhaustive list of these additional units is as follows:

and R₃, which can be identical or different, each have the definition given above for R₁, the units (I˝) being able to be identical or different between them,

symbol A has the meaning given above in connection with the units (IV).

• (V) désignant la structure :
  
• (VI) désignant la structure :
  

- la quantité des unités (V) dans le mélange (V) + (VI) se situe dans l'intervalle allant de 10 à 90 % en mole et celle des unités (VI), par rapport à la même référence, se situe dans l'intervalle allant de 90 à 10 % en mole ;
. S'agissant des polyesteramides :
- ils comprennent des unités de récurrence de formules (VII), (VIII) et (IX) :

• (VII) désignant la structure :
  
• (VIII) désignant la structure :
  
• (IX) désignant la structure :
  

- la quantité des unités (VII) dans le mélange (VII) + (VIII) + (IX) se situe dans l'intervalle allant de 10 à 90 % en mole, celle des unités (VIII), par rapport à la même référence, se situe dans l'intervalle allant de 5 à 45 % en mole et celle des unités (IX), par rapport à la même référence, se situe dans l'intervalle allant de 5 à 45 % en mole.Another type of completely aromatic thermotropic polyesters and polyesteramides which are also very particularly preferred for the implementation of the present invention consists of the polymers described in US Pat. Nos. 4,161,470 and 4,330,457 which have the following characteristics:
. Regarding polyesters:
- they include recurrence units of formula (V) and (VI):

• (V) designating the structure:
  
• (VI) designating the structure:
  

- the quantity of the units (V) in the mixture (V) + (VI) is in the range from 10 to 90% by mole and that of the units (VI), with respect to the same reference, is in the range from 90 to 10 mol%;
. With regard to polyesteramides:
- they include recurrence units of formulas (VII), (VIII) and (IX):

• (VII) designating the structure:
  
• (VIII) designating the structure:
  
• (IX) designating the structure:
  

- the quantity of the units (VII) in the mixture (VII) + (VIII) + (IX) is in the range from 10 to 90 mol%, that of the units (VIII), with respect to the same reference , is in the range from from 5 to 45% by mole and that of the units (IX), with respect to the same reference, lies in the range going from 5 to 45% by mole.

Among the completely aromatic polyesters and polyesteramides belonging to this other group of very especially preferred polymers, those which are very suitable are the polymers placed on the market by the company CELANESE, under the registered trademark VECTRA, of type A 900 (polyester) or B 900 (polyesteramide).

As crystalline mineral fillers of platelet shape, having an average diameter which is in the range of 0.5 to 400 µm and having a form factor which is in the range of 10 to 90, which are used from preferably, particular mention will be made of: mica, natural talc, calcined talc or a mixture of these species.

The mica used can belong to one or other of the following families and genera: white mica, genus: in particular muscovite, phengite and paragonite; black mica, genus: especially biotite and phlogopite; pink mica, genus: especially lepidolite. As for talc, with the chemical formula Mg₃ Si₄ O₁₀ (OH) ₂, it can in particular belong either to the iron variety or to the nickeliferous variety. The mineral filler according to the present invention can also be talc having undergone a calcination treatment. This treatment consists in heating the talc chosen to a temperature at least equal to 500 ° C, more precisely lying between 800 ° C and 1100 ° C by operating in ambient air, under nitrogen atmosphere or under humid air atmosphere. ; one can work in a static oven, in a rotary oven or in a flash calcination device, for a period ranging for example from 2 hours to 5 hours.

The use of mica corresponds to a particularly advantageous embodiment of the invention. The use of black mica belonging to the phlogopite genus, to reinforce the thermotropic polymer, corresponds to an embodiment of the invention which is more particularly advantageous.

Usually, in the case of mica, use is made of a filler comprising scales whose mean diameter is between 10 μm and 400 μm and, preferably, between 20 μm and 300 μm; in the case of talc, natural or calcined, use is made of a filler comprising particles whose average diameter is between 0.5 μm and 100 μm and, preferably, between 1 μm and 15 μm. As for the form factor, it is preferably between 30 and 90 in the case of mica and between 10 and 30 in the case of talc, natural or calcined.

The amounts of mineral reinforcing filler to be used to prepare the compositions according to the invention are those indicated above in the present specification. Note that the minimum limit of these quantities must be increased from 20 to a value greater than 50% and more specifically from 20 to 51% when the average particle diameter is less than 20 µm (this is particularly the case when the commercial talcs are used), so that the filler produces the desired technical effect which is presented above for the first object of the invention. Very satisfactory results in terms of anisotropy (RA and sum ML + MT) are obtained with amounts of mineral filler which are preferably in the range ranging from 20% to 50% by weight when the average diameter of the particles is 20 µm or more; in the case where this average diameter is much less than 20 μm, like an average diameter between 1 μm and 15 μm, the very satisfactory results which we have just spoken of correspond to quantities of mineral filler which are preferably situated in the range from 55% to 60% by weight.

An even more particularly advantageous embodiment of the invention therefore consists in using mica having an average diameter of between 20 μm and 300 μm and a form factor of between 30 and 90, this mineral filler being used in amounts in the range of 20% to 50% by weight.

Another interesting embodiment of the invention also consists in using natural talc having an average diameter between 1 μm and 15 μm and a form factor lying between 10 and 30, this mineral filler being used in amounts in the range of 55% to 60% by weight.

Si - O - R₄ dans lequel R₄ représente un reste alkyle inférieur capable de se lier avec la charge minérale et au moins un autre groupe capable de se lier avec le polymère. Avec les polymères thermotropes de la présente invention, cet autre groupe fonctionnel peut être un groupe amino ou un groupe époxy. Des exemples de composés organosiliciques qui conviennent sont : le γ -aminopropyltriméthoxysilane, le γ -aminopropyltriéthoxysilane, le N-(β -aminoéthyl) γ -aminopropyltriméthoxysilane, le β -(époxy-3,4 cyclohexyl)éthyltriméthoxysilane, le γ -glycidoxypropyltriméthoxysilane.The compositions according to the present invention may further comprise, and this is a measure which may be advantageous in particular in the case of the use of mica and / or calcined talc, a coupling agent. This coupling agent is usually chosen from polyfunctional organosilicon compounds. These compounds include at least one alkoxysilane group

Si - O - R₄ in which R₄ represents a lower alkyl residue capable of binding with the mineral filler and to least one other group capable of bonding with the polymer. With the thermotropic polymers of the present invention, this other functional group can be an amino group or an epoxy group. Examples of suitable organosilicon compounds are: γ -aminopropyltrimethoxysilane, γ -aminopropyltriethoxysilane, N- (β -aminoethyl) γ -aminopropyltrimethoxysilane, β - (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-propyl.

The amount of coupling agent required to ensure a good bond between the mineral reinforcing filler and the base polymer is relatively small. Only 0.1% of coupling agent based on the weight of the filler may be sufficient. In general, amounts of coupling agent of between 0.3% and 4% appear to be very satisfactory.

The reinforced thermotropic polymer compositions according to the present invention can be prepared in various ways known per se.

The mixing of the various constituents can be carried out for example in two periods: a first period in which the various constituents are stirred together at room temperature (23 ° C) in a conventional powder mixer (which can simply be the feed hopper of 'an extruder) and a second period in which this premix is homogenized by hot mixing at a temperature above 200 ° C in an extruder with one or more screws. It is possible, if necessary, between these two periods, to carry out drying to a variable degree of the premix obtained at the end of the first period. After these treatments, the compositions of the invention are generally transformed into granules which will be used subsequently for shaping the desired articles by operating in conventional molding machines.

In the case where a coupling agent is used, the latter can be incorporated into the preparation medium of the compositions according to the invention in different ways: according to a first variant, the coupling agent can be deposited beforehand on the filler which will serve to reinforce the polymer; according to a second variant, the coupling agent can be deposited beforehand on the polymer before the addition of the filler; according to a third variant, the coupling agent can be mixed directly with the polymer and the filler. In view of the above, the expression "various constituents", which appears above in connection with the method of preparation of the compositions according to the invention, will mean: variant 1: pretreated mineral filler + polymer; variant 2: mineral filler + pretreated polymer; variant 3: polymer + mineral filler + coupling agent.

The treatment with the coupling agent, when one is used, is usually carried out by direct or progressive incorporation of the latter, in the pure state or dissolved in an appropriate solvent, in the feed (variant 1), in the polymer (variant 2) or as a whole filler + polymer (variant 3). In the case of variant 1 in particular, it is possible to treat the charge by the technique of mixing in a fluidized bed or by the technique employing a rapid mixer.

The polymer compositions according to the invention can also be prepared by making a masterbatch, presented in the form of granules or of paste based on a part of the polymer to be reinforced, of filler and possibly of coupling agent, which will be mixed. then before implementation with granules or a paste of the rest of the polymer to be reinforced.

The compositions according to the invention may also contain one or more additives such as, for example, pigments, stabilizers, nucleating agents, flow characteristics modifiers and flame retardants. The incorporated amounts of these additives do not generally exceed 40% of the weight of the polymer matrix.

The compositions according to the invention can then be injection molded according to general practice using known techniques and operating within the anisotropy range of the thermotropic polymer. It will be noted that the thermotropy is easy to demonstrate when the polymer is observed in the molten state in an optical system equipped with two crossed polarizers (90 ° angle): there is a birefringence for the anisotropic samples and transmission of polarized light through crossed polarizers. The demonstration of the anisotropy of the thermotropic polymers according to the present invention was carried out by the TOT thermo-optical method described in French patent 2,270,282. The term "anisotropy range" means the interval of temperature which starts from the temperature at which the birefringence and the transmission of light appears through the two crossed polarizers and which is situated above said temperature, interval having a variable upper limit and in which the melt is anisotropic without any risk of polymer decomposition. In general, the anisotropic melts which are targeted in the context of the present invention have an anisotropy range spread over at least 30 ° C.

The shaped articles obtained have at least the following two properties:
- the anisotropy ratio (AR) is reduced by at least 50%; for example, a reduction rate of the RA of 67.7% can be achieved with only 26.7% by weight of black mica of the genus phlogopite marketed by the Company MARIETTA under the name SUZORITE 60 S; and
- Furthermore, the sum ML + MT is at least equal to 1.5 times the value of the same sum obtained in the case of the uncharged polymer; for example, in the case of the particular charge mentioned above, this sum is equal to 2.09 times the value taken as reference.

The nonlimiting examples which follow show how the present invention can be practiced practically.

EXAMPLES 1 TO 6 AND COMPARATIVE TESTS A - F: 1. Description of the thermotropic polymer used

An aromatic copolyester of the type described in European patent application No. 86420013.4 published under No. 0.191.705 is prepared.

• (1) diacétate de méthylhydroquinone : 1456 g
  rapport molaire (1)/(2) + (3) = 1
• (2) acide téréphtalique : 581 g
  50 % en mole dans mélange (2) + (3)
• (3) dicarboxy-4,4′ diphényléther : 903 g
  50% en mole dans mélange (2) + (3)
• (4) acide para-acétoxybenzoïque : 756 g
  60 % en mole par rapport à (1).

In a 7.5 liter polycondensation reactor stirred and heated by a heat transfer fluid circulating in the double jacket of the reactor, provided with a device for distillation and scanning with an inert gas, the following reagents are introduced:

• (1) methylhydroquinone diacetate: 1456 g
  molar ratio (1) / (2) + (3) = 1
• (2) terephthalic acid: 581 g
  50% by mole in mixture (2) + (3)
• (3) dicarboxy-4,4 ′ diphenyl ether: 903 g
  50% by mole in mixture (2) + (3)
• (4) para-acetoxybenzoic acid: 756 g
  60% by mole relative to (1).

The reactor is purged with nitrogen, then heated by the heat transfer fluid adjusted to 260 ° C for 2 hours and 20 minutes. The volume of distilled acetic acid is 890 cm³ (85% of theory). The temperature of the heat transfer fluid is then gradually raised to 300 ° C. in 60 minutes, at the same time reducing the pressure from 1010.10² Pa to 0.39.10² Pa. After the distillation of acetic acid has stopped, the temperature of 300 ° C. and the pressure of 0.39 × 10 2 are still maintained for 39 minutes. The total volume of acetic acid collected is 1040 cm³ (ie 100% of theory).

The polymer obtained is grayish and fibrous in appearance. It has an inherent viscosity of 2.07 dlg⁻¹. The flow temperature is 290 ° C. The anisotropy range is from 290 ° C to over 350 ° C.

2. Production of the compositions according to the invention

The thermotropic copolyester obtained is used to prepare different compositions loaded with micas of different natures in variable proportions which are those indicated in Table 1 given below.

The general procedure for preparing these compositions is as follows:
. By operating in an ELTE 650 roller mixer from the ENGELSMANN company, the thermotropic polymer and the mineral filler are brought into direct contact at room temperature. The micas used belong to the family of black mica, genus: phlogopite; they are marketed by the MARIETTA Company under the names:
- SUZORITE 60 S: the average diameter is 280 µm and the form factor is 68;
- SUZORITE 150 S: the average diameter is 150 µm and the form factor is 47; and
- SUZORITE 325 S: the average diameter is 22 µm and the form factor is equal to 33.

The premix prepared with each of the aforementioned micas is then allowed to dry in an oven brought to 160 ° C for 16 hours, under a pressure reduced by 1.33.10² Pa.
. The pre-steamed premix is then kneaded in the molten state in an LEISTRITZ brand extruder comprising two co-rotating screws with a diameter D equal to 34 mm and a length equal to 35 D; the profile of the screws is suitable for working with aromatic polyesters; the extruder is equipped with a die with a hole of 4 mm in diameter; the conditions of the extruder are as follows: - die temperature : 310 ° C, - screw rotation speed : 200 rpm, - material flow : about 10 kg / h.

The product collected in the form of a rod is cooled in ambient air, then it is granulated and dried.

From the granules obtained, square plates of dimensions 100 × 100 × 2 mm are prepared which are injection molded. This molding is carried out using a screw-piston machine of the BATTENFELD brand type BSKM 100/70 DS 2000 under the following conditions: - material temperature : 290 ° C, - mold temperature : 100 ° C, - injection pressure : 65.10⁵ Pa, - holding pressure : 25.10⁵ Pa, - duration of an injection cycle : 30 sec.

The test pieces, whose shape and dimensions correspond to those defined by the standard mentioned below, are taken from the molded plates obtained in order to carry out bending tests: the bending module is measured at 23 ° C. on conditioned test pieces at EH O (zero% relative humidity) according to the indications of standard NE T 51001 (the test pieces are placed in a desiccator on silica gel and dried again 24 hours at room temperature under a reduced pressure of 0.67 × 10 2 to 1, 33.10² Pa before performing the measurements); it should be noted that this mechanical property was measured on samples taken on the one hand longitudinally (direction of the injection) and on the other hand transversely (direction perpendicular to the injection). The results of the bending tests are shown in Table 1 below.

By way of comparative tests, the same operations were reproduced as those described above, but:
- test A: without using a mineral filler and therefore not pre-mixing,
- tests B, C and D: using amounts of mica which lie outside the range of values according to the present invention.

By way of other comparative tests, the same operations were reproduced as those described above, but this time using, in place of the mica, a comparable quantity:
- test E: of glass fibers having an average length of 4500 μm and an average diameter of 15 μm, sold by the company OWENS CORNING FIBERGLAS under the reference 429 YZ; and
- test F: of wollastonite having an average fiber length of 75 μm and an average diameter of 25 μm, marketed by the company PARAISTEN KALKKIOY. TABLE 1 EXAMPLE / TEST NATURE OF THE LOAD LOAD QUANTITY BENDING MODULE GPa % Weight % Volume ML MT ML / MT anisotropy report Sum ML + MT AT - 0 0 9.8 2.1 4.67 11.9 B MICA 60 S 10.7 5.7 11.7 4.6 2.54 16.3 1 MICA 60 S 26.7 15.4 15.0 9.9 1.51 24.9 VS MICA 150 S 11.0 5.9 11.4 4.0 2.85 15.4 2 MICA 150 S 29.6 17.4 13.0 8.3 1.57 21.3 3 MICA 150 S 44.5 28.6 18.1 14.2 1.27 32.3 D MICA 325 S 9.7 5.1 10.4 3.7 2.81 14.1 4 MICA 325 S 24.6 14.0 12.5 7.1 1.76 19.6 5 MICA 325 S 40.7 25.5 16.1 12.4 1.29 28.5 6 MICA 325 S 48.2 31.8 18.5 14.3 1.29 32.8 E FIBERGLASS 28.5 18.7 11.1 5.4 2.06 16.5 F WOLLASTONITE 26.2 15.0 10.1 3.6 2.81 13.7 ML = longitudinal modulus in flexion. MT = transverse module in bending.

EXAMPLE 7 AND COMPARATIVE TESTS G, H AND I:

• (1) diacétate de chlorohydroquinone : 1028 g
  rapport molaire (1)/(2) + (3) = 1
• (2) acide téréphtalique : 373 g
  50 % en mole dans mélange (2) + (3)
• (3) dicarboxy-4,4′ diphényléther : 581 g
  50 % en mole dans mélange (2) + (3)
• (4) acide para-acétoxybenzoïque : 275,5 g
  34 % en mole par rapport à (1)
• (5) acétate de magnésium : 1,13 g
  500 ppm.

Le réacteur est purgé à l'azote, puis chauffé par le fluide caloporteur réglé à 260°C pendant 2 heures et 20 minutes. Le volume d'acide acétique distillé est de 506 cm³ (soit 83 % de la théorie). On élève ensuite progressivement la température du fluide caloporteur jusqu'à 330°C en 40 minutes, en diminuant dans le même temps la pression de 1010.10² Pa à 0,39.10² Pa. Après que la distillation d'acide acétique se soit arrêtée, on maintient encore la température de 330°C et la pression de 0,39.10² pendant 12 minutes 30 secondes. Le volume total d'acide acétique recueilli est de 602 cm³ (soit 100 % de la théorie). Le polymère obtenu est grisâtre et d'aspect fibreux. 51 possède une viscosité inhérente de 1,4 dlg⁻¹. La température d'écoulement est de 290°C. La plage d'anisotropie va de 290°C jusqu'à plus de 350°C ;
. et, à la place du mica, diverses quantités de talc naturel comercialisé par la Société des TALCS DE LUZENAC sous la dénomination 15 M 00 ; le diamètre moyen des particules est de 8 µm et le facteur de forme est de l'ordre de 20.The same operations were reproduced as those described in Example 1, but this time using:
. instead of the thermotropic polymer in accordance with European patent application No. 86420013.4 derived from methylhydroquinone diacetate, the thermotropic polymer of the same type derived from chlorohydroquinone diacetate; The following reactants and catalysts are now introduced into the reactor described in Example 1, paragraph 1:

• (1) chlorohydroquinone diacetate: 1028 g
  molar ratio (1) / (2) + (3) = 1
• (2) terephthalic acid: 373 g
  50% by mole in mixture (2) + (3)
• (3) dicarboxy-4,4 ′ diphenyl ether: 581 g
  50% by mole in mixture (2) + (3)
• (4) para-acetoxybenzoic acid: 275.5 g
  34% by mole compared to (1)
• (5) magnesium acetate: 1.13 g
  500 ppm.

The reactor is purged with nitrogen, then heated by the heat transfer fluid adjusted to 260 ° C. for 2 hours and 20 minutes. The volume of distilled acetic acid is 506 cm³ (or 83% of theory). The temperature of the heat transfer fluid is then gradually raised to 330 ° C in 40 minutes, at the same time reducing the pressure from 1010.10² Pa to 0.39.10² Pa. After the distillation of acetic acid has stopped, the temperature of 330 ° C. and the pressure of 0.39 × 10 2 are still maintained for 12 minutes 30 seconds. The total volume of acetic acid collected is 602 cm³ (or 100% of theory). The polymer obtained is grayish and fibrous in appearance. 51 has an inherent viscosity of 1.4 dlg⁻¹. The flow temperature is 290 ° C. The anisotropy range is from 290 ° C to more than 350 ° C;
. and, in place of mica, various quantities of natural talc marketed by the TALCS DE LUZENAC Company under the name 15 M 00; the average particle diameter is 8 µm and the form factor is around 20.

The quantities of talc used, which are within the range of values according to the present invention for example 7, but which are outside this range for tests H and I, and the mechanical properties of the articles obtained are collated in the following table 2. In this table, we will also find the results of the control test G conducted without using talc. TABLE 2 EXAMPLE / TEST QUANTITY OF TALC BENDING MODULE GPa % Weight % Volume ML MT ML / MT anisotropy report Sum ML + MT G 0 0 11.0 2.0 5.50 13.0 H 25 15 12.0 4.0 3.00 16.0 I 30 18 11.0 4.5 2.44 15.5 7 60 43 10.5 9.5 1.11 20.0

EXAMPLES 8 AND 9 AND COMPARATIVE TESTS J AND K:

The same operations were reproduced as those described above in Example 1, but this time using thermotropic polymers sold by the company CELANESE under the brand VECTRA:
- Example 8: the polymer used is of type A 900 and it is a polyester comprising repeat units oxy-6 naphthoyl-2 (about 20% by mole) and paraoxybenzoyl (about 80% by mole);
- Example 9: the polymer used is of type B 900 and it is a polyesteramide comprising oxy-6 naphthoyl-2, terephthaloyl and paraaminobenzoyl recurrence units.

The mineral filler used in these two examples is black mica, genus: phlogopite, sold under the name SUZORITE 60 S and its use amounts are in both cases equal to 40% by weight.

By way of comparative tests, the same operations were reproduced, but without using a mineral filler: test J with the polymer of pure type A 900; and test K with the pure type B 900 polymer.

The mechanical properties of the objects obtained are collated in Table 3 below. TABLE 3 EXAMPLE / TEST NATURE OF MICA QUANTITY OF MICA BENDING MODULE GPa % Weight % Volume ML MT ML / MT anisotropy report Sum ML + MT J - 0 0 10.7 2.9 3.69 13.6 8 60 S 40 28.6 19.15 10.8 1.77 29.9 K - 0 0 17.3 4.3 4.02 21.6 9 60 S 40 28.6 26.9 13.8 1.95 40.7

Claims (9)

1 / Molding compositions which include:
a) a thermotropic polymer, and
b) a mineral reinforcing filler,
characterized in that the mineral filler (b) meets the following definitions:
. it belongs to the family of crystalline mineral fillers of platelet form having an average diameter which is in the range from 0.5 to 400 μm and a form factor represented by the ratio:

which is in the range of 10 to 90;
. it is implemented using use quantities, expressed in% by weight of filler in the polymer + filler assembly, which are in the range from 20% to 60%, with the additional condition that these quantities are in the range from a value greater than 50% up to 60% when the average particle diameter is less than 20 µm. 2 / Compositions according to claim 1, characterized in that the thermotropic polymers which are suitable are fully aromatic polyesters, alkylaromatic polyesters, fully aromatic polyesteramides, alkylaromatic polyesteramides, aromatic polyazomethines, aromatic polyester carbonates and mixtures of these polymers . 3 / Compositions according to claim 2, characterized in that the thermotropic polymers which are used are fully aromatic polyesters, fully aromatic polyesteramides and mixtures of these polymers. 4 / Compositions according to any one of Claims 1 to 3, characterized in that the thermotropic polymers have a flow temperature in the range of 200 ° C to 350 ° C and have an inherent viscosity at least equal to 0.5 dlg⁻¹. 5 / Compositions according to any one of claims 1 to 4, characterized in that the crystalline mineral filler of platelet form which is used consists of mica, natural talc, calcined talc or a mixture of these species. 6 / Compositions according to claim 5, characterized in that one uses mica. 7 / Compositions according to any one of claims 1 to 6, characterized in that they can further comprise, next to the thermotropic polymer a) and the mineral filler b), a coupling agent consisting of a polyfunctional organosilicon compound comprising at least one alkoxysilane group capable of binding with the mineral filler and at least one group capable of binding with the polymer a). 8 / shaped articles made by molding from the compositions according to any one of the preceding claims 1 to 7. 9 / Articles according to claim 8, characterized in that they have at least the following two properties:
- the anisotropy ratio (AR) is reduced by at least 50%;
- In addition, the sum ML + MT is at least equal to 1.5 times the value of the same sum obtained in the case of the uncharged polymer.